The present invention relates to a process for the construction of walls of mortar based on earth and sand with a small admixture of bonding materials, i.e. mixtures which are generally referred to as cobs; projecting apparatus which is specifically suitable for the application of this process; and a wall thus obtained.
Cobs find application in particular in the field of buildings and public works, for example:
- the construction of the walls of buildings for various purposes, the walls of dwelling-houses, and enclosing walls, PA0 - the renovation of the facades of old houses constructed on the basis of earth (cobs, daub, clay and straw, air-dried bricks, etc.), PA0 - the facing of any facades of buildings or enclosing walls worked in a traditional manner (composite blocks, concrete screens, diverse bricks), PA0 - the forming of various slopes and embankments of soil. PA0 - making up a mixture containing between 15 and 50% by mass of earth and 85% and 50% by mass of sand, to which is added a quantity of bonding materials representing at most 10% of the dry mass of aggregates (earth and sand), as well as water, representing at most 22% of the total dry mass (earth and sand and bonding materials); PA0 - stirring the mixture continuously and transferring it, preferably by force, to the inlet of a pump; PA0 - pumping the mixture and projecting it against a projection support (Preferably, the projection support is a removable wall which is removed after setting of the mortar). PA0 a) By virtue of a new design of the shape of the outer casing of the supply tank by adjusting the "body" of the casing to be closer to the group of internal movable parts, in order to eliminate dead spaces. PA0 b) By virtue of the application of an overall system for continuous mixing. The system comprises a set of two contrarotating mixers (there may be two or more such mixers, but for reasons of economy these are preferably limited by example herein to two) on parallel horizontal axes, and having overlapping sweep zones (the sweep zones overlapping by preferably three-quarters). This set is itself placed immediately above a supply impeller and close to the sweep zone of the latter. This arrangement at least reduces the danger of the formation of an air pocket above and adjacent to the supply impeller, due to the erratic movements of the continuously-agitated mortar. This erratic effect is capable of being intensified by the ability to reverse instantaneously and at any given moment the direction of rotation of the set of mixers, owing to the flexibility of the associated hydraulic transmission. PA0 c) In similar fashion, the supply impeller, having stub blades or a screw conveyor, operates within a semi-tubular sheet-metal duct arranged close to the sweep zone of the impeller, and placed directly below the full length of the supply tank and the set of mixers. This semi-tubular duct encases the "lower two-thirds" of the sweep zone of the supply impeller, while leaving the "upper one-third" free to open directly into the supply tank and the set of mixers. PA0 a) This chamber projects from the main body of the machine and is arranged in direct alignment with the semi-tubular casing of the supply impeller, without having any dead space or interruption in the continuity of the flow of fluids in the course of transit. This chamber advantageously takes the form of a tubular casing of sheet-metal or cast-iron, arranged around the sweep zone of the extension of the impeller, thus performing the function of a passage for forcing the mortar to the pump. PA0 b) Simultaneously, this chamber performs the function of a decompression chamber and of clearing out of the sand resulting from a possible segregation and tending to accumulate at the supply orifice of the pump. For that purpose, the chamber preferably comprises at least one inspection door of the movable cover type. Two inspection doors are advantageously placed in opposition on opposite sides of the chamber the doors opening vertically or laterally, for the purpose of rapid cleaning out of plugs of sand.
"Cobs" are mortars based on soil which is frequently clayey, and sand mixed in varying proportions according to the nature of the soil, with an admixture of bonding materials determined in terms of the dry mass of the initial aggregates (earth and sand) and an admixture of water.
These mortars are then normally placed between two parallel boards and tamped by hand with a rammer, resulting in an increased application time and thus affecting costs. This explains the virtual disappearance of this technique since 1945.
Other variations on the basis of stabilized earth have also been suggested, which variations call for the making of air-dried bricks by pressing; these bricks are then placed in position in known manner, which entails the costs of manual labour very similar to those of conventional concrete blocks (Rollow agglomerates).
Machines suitable for projecting compositions of mortars by a process referred to as "wet" (the mortar receiving its final supply of water before passing into the machine) are known, for example according to the principle of the "MOINEAU" pump (this includes a steel rotor in the form of "a pig's tail", rotating in a stator of flexible matter such as rubber or the like, sheathing the inner surface of a tubular duct of steel or cast iron). These machines frequently comprise an hydraulic transmission system enabling the simple and quick reversal of the direction of rotation of all the movable parts (in particular impeller, pumps). This is the case, inter alia, in the PRECIJET H 3000 machine of MIXJET FRANCE, the MF 80 HY of MOSSMER, and the P13 of PUTZMEISTER. However, these machines work properly only with microconcretes which have a high content of binding material (in the order of 20 to 30%) and which are very liquid. These types of mortars can be applied only in successive thin layers of about 0.5 to 2 cm, and can therefore in fact be used only for extra-thin facings of facades or concrete coatings on latticed supports of the STUCANET or NERGALTO type.
Various designs of projecting machines already on the market are not technically workable, and therefore even less commercially viable, due to numerous operational difficulties, for the projection of cob mortars with lower contents of binding materials and water, which are nevertheless necessary for the making of very thick walls (layers of more than 5 cm in thickness placed into position in one single operation on a movable, light, bottom support).
Such mortars with a low admixture of binding materials and water, in fact bring about the rapid formation of an air pocket in currently used machines, at the level of the mixture of the cob mortar in the supply tank of the machine adjacent and above the supply impeller. This causes the frequent loss of priming of the mortar pump and the need to drain the supply tank completely, in order to "break" the arch of mortar hanging over the impeller, thus causing the complete loss of the batch in progress and causing a considerable loss of operational time.
Also the low content of binding material brings about a rapid segregation of part of the sand from the cob-mortar mixture statically waiting in the supply tank of the main body of the machine; this sand then accumulates in non-elastic plugs in the dead spaces of the supply tank and in particular at the inlet of the supply orifice of the mortar pump, this providing a further cause for the loss of priming of the pump, and even the danger of a complete blockage of the entire machine. This results in a renewed need to drain the supply tank to enable the cleaning of the approaches to the supply orifice of the pump.
Finally, in the event of a delay in carrying out the projection of the mixture statically waiting in the supply tank, drying of the mixture occurs and the mortar commences to set, thus aggravating the formation of arches and air pocket effects adjacent the supply impeller, in particular in the case of supply tanks having a V-shape, which are presently used.
The invention has the aim of alleviating these disadvantages.